The enhancement of engine performance that can be attained by varying the valve timing and lift as well as the acceleration, velocity and travel time of the intake and exhaust valves in an internal combustion engine is well known and appreciated in the art. Further, many contemporary engines are multi-valve engines that employ, for example, four valves per cylinder, i.e., 2 intake and two exhaust valves, to improve overall engine performance. As used herein, the term multi-valve engine means more than just one intake and one exhaust valve per cylinder in the engine, (i.e., a three-valve, four-valve, or five-valve per cylinder engine), although generally four valve per cylinder engines will be discussed herein.
In a four valve engine with an electrohydraulic valve train system that independently controls each engine valve, the balancing of valve lift can be performed by varying the electrical signals going to the different control means. However, independently controlling each engine valve with separate hydraulic valve controls is expensive and can require excessive space.
To reduce the number of hydraulic valve controls, the engine valves within a cylinder performing the same functions can be coupled together. That is, the pair of intake valves in each cylinder can be operated with the same hydraulic valves and controls; as well, the pair of exhaust valves in each cylinder can be similarly coupled together. It is desirable to be able to activate each pair of engine valves with substantially the same lift and timing for most engine operating conditions. But this is not always possible because of tolerances in manufacturing, viscous drag and other contributing factors that create slight differences between each engine valve in any given pair.
The need, then, arises for an electrohydraulic valvetrain that will work in a four valve (or other multi-valve) engine to ensure substantially identical lift and timing of each pair of engine valves when necessary, while not requiring separate independent controls for each engine valve in the valvetrain.